It is known to those skilled in the art that ethers, including both symmetrical and unsymmetrical ethers, may be prepared by reacting an alcohol with another alcohol to form the desired product. The reaction mixture, containing catalyst and/or condensing agent may be separated and further treated to permit attainment of the desired product. Such further treatment commonly includes one or more distillation operations.
Of the ethers which can be produced, a great deal of attention has been directed toward the production of methyl tertiary butyl ether (MTBE) for use as a gasoline oxygenate.
U.S. Pat. No. 4,918,244, to Nelson et al., discloses a method of preparing MTBE by continuously feeding t-butyl alcohol and methanol into a solid-acid catalyst bed, in a reactor separator rectification column in the presence of a solid acid catalyst, such as Amberlyst.RTM. 15, whereby a product of substantially pure methyl tertiary butyl ether (MTBE) is separated from the reaction mixture.
An article titled "Expanding Refinery Technology leads to New Ether Potential," by William J. Peil, Fuel Reformulation, (1992, November/December) p. 34, contains a good review of the potential of ethers other than MTBE for use in meeting the EPA's requirements.
Though MTBE is the most widely produced and discussed ether, other ethers are also being evaluated, such as diisopropyl (DIPE) and ethyl tertiary butyl ether (ETBE). DIPE can be produced from refinery propylene and water with isopropanol as an intermediate in this process. In a variation, isopropyl tertiary butyl ether could be produced by combining isobutylene with isopropanol.
DIPE has similar physical and blending activities to MTBE and TAME and is a perfectly acceptable fuel oxygen source. Wood, A., Chemical Week, Apr. 15, 1992, p. 7.
The higher molecular weight ethers all have blending vapor pressures lower than MTBE, and much lower than ethanol. Their boiling temperatures are also higher than MTBE. Furthermore, higher molecular weight IPTBE has the potential to contribute more octane.
Although there has not been as much discussion regarding the production of IPTBE as there has been for MTBE, it is apparent that with its lower oxygen level and lower vapor pressure, there should be a definite niche for IPTBE in the future of reformulated gasoline.
The .beta.-zeolite catalysts found useful in this integrated process for production of IPA, DIPE, MTBE and IPTBE have been known in the art for some time. One of the earliest disclosures of zeolite beta was in U.S. Pat. No. 3,308,069 (1967) to Wadinger et al.
J. B. Higgins, et al. of Mobil Research and Development published an article in Zeolites, 1988, Vol. 8, November, 446-452 titled "The Framework Topology of Zeolite Beta." In the article Higgins et al. disclose what is known about the framework topology of zeolite beta. The information was determined using a combination of model building, distance-least-square refinement and powder pattern simulation.
In an article titled "Cumene Disproportionation over Zeolite .beta. I. Comparison of Catalytic Performances and Reaction Mechanisms of Zeolites," Applied Catalysis, 77 (1991) 199-207, Tseng-Chang Tsai, Chin-Lan Ay and Ikai Wang disclose a study demonstrating that cumene disproportionation can be applied as a probe reaction for zeolite structure. It is revealed that zeolite beta would have application potential in the production of diisopropylbenzene for reasons of activity, selectivity and stability.
In a second part of the article, "II. Stability Enhancement with Silica Deposition and Steam Pretreatment", Ibid, pp. 209-222, Tsai and Wang disclose their development of two methods to improve the stability of zeolite beta, silica deposition and steam pretreatment.
Zeolites of low acidity can be achieved by a variety of techniques including steaming. In the case of steaming the zeolite can be exposed at elevated temperatures, 500.degree. to 1200.degree. F., preferably (750.degree. to 1000.degree. F.). This treatment is accomplished in 100% steam or an atmosphere of steam and gas which is substantially inert to the zeolite. A similar treatment can be accomplished at a lower temperature using elevated pressure, e.g., from about 350.degree. F. to 700.degree. F. at from about 10 to 200 atmospheres. Specific details of several steaming procedures can be gained from the disclosures of U.S. Pat. Nos. 4,325,994; 4,374,296 and 4,418,235.
Patents in the art which employ zeolite beta relate mainly to dewaxing, and cracking of hydrocarbon feedstock.
An article titled "Beta Zeolite as Catalyst or Catalyst Additive for the Production of Olefins During Cracking or Gas Oil," was written by L Bonetto et al., 9th International Zeolite Conference, July 1992, FP 22. The authors note that with the greater demand for oxygenated compounds there is indication there might be increased demands for catalysts and conditions which maximize C.sub.3, C.sub.4 and C.sub.5 olefins. They suggest that .beta.-zeolite could be used alone or combined with Y-zeolite as a suitable zeolite component. Various catalysts were studied with respect to minimization of diffusional requirements and zeolite stability.
U.S. Pat. No. 4,419,220, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing straight chain paraffins which comprises contacting the feedstock with a .beta.-zeolite catalyst having a Si:A1 ratio of at least 30:1 and a hydrogenation component under isomerization conditions.
Another European Application to Mobil, EP 0 094 82, discloses simultaneous catalytic hydrocracking and hydrodewaxing of hydrocarbon oils with .beta.-zeolite.
In European Patent Application 0 095 303, to Mobil, there is a disclosure of dewaxing distillate fuel oils by the use of .beta.-zeolite catalysts which, preferably have a silica:alumina ratio over 100:1. Ratios as high as 250:1 and 500:1 are disclosed as useful.
Another U.S. Pat. No. 4,518,485, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing paraffins selected from the group of normal paraffins and slightly branched paraffins and sulfur and nitrogen compounds where, after conventionally hydrotreating the feedstock to remove sulfur and nitrogen, the hydrotreated feedstock is dewaxed by contacting the feedstock with a catalyst comprising a .beta.-zeolite having a silica/alumina ratio of at least 30:1.
In U.S. Pat. No. 4,740,292, to Mobil, there is disclosed a catalytic cracking process which comprises cracking a hydrocarbon feed in the absence of added hydrogen with a cracking catalyst comprising a .beta.-zeolite component and a faujasite component comprising at least one crystalline aluminosilicate of the faujasite structure, the weight ratio of the faujasite component to the .beta.-zeolite component being from 1:25 to 20:1.
Large pore .beta.-zeolite has been employed in the synthesis of industrially important para-cumene by toluene isopropylation. See "Toluene Isopropylation over Zeolite .beta. and Metallosilicates of MFI Structure," P. A. Parikh et al., Applied Catalysis, A, 1992, 90, p. 1.
In European Patent 323 138 and U.S. Pat. No. 4,906,787, there is disclosed a catalytic process for converting light olefins to ethers suitable as high octane blending stocks carried out by contacting the olefin, especially propene, with water and alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst. In this work diisopropyl ether (DIPE) was prepared from C.sub.3 H.sub.6 and aqueous iso-PrOH in the presence of silica-bound zeolite Beta catalyst at 166.degree. C.
In U.S. Pat. No. 5,144,086, to Harandi et al., there is disclosed an integrated multistage process for the production of diisopropyl ether from substantially pure propene wherein in the second stage isopropanol containing about 0-20% water is contacted with an acidic large pore zeolite etherification catalyst which comprises a .beta.-zeolite having a silica to alumina ratio of about 30:1 to 50:1.
In a European Patent, EP 323 268, light olefins are converted to alcohols and/or ethers in the presence of .beta.-zeolite.
U.S. Pat. No. 4,058,576 to Chang et al. teaches the use of (pentasil-type) aluminosilicate zeolites, such as ZSM-5, having a pore size greater than 5 angstrom units and a silica-to-alumina ratio of at least 12, to convert lower alcohols to a mixture of ethers and olefins.
U.S. Pat. No. 4,714,787, to Bell et al., discloses a process for the manufacture of methyl isopropyl ether from methanol and a C.sub.3 hydrocarbon fraction that contains 20 to 100 wt. % of propylene, which process comprises preparing a mixture of said hydrocarbon fraction and 0.1 to 10 moles of methanol per mol of propylene contained in said fraction, contacting said mixture with a solid insoluble acid catalyst comprising materials having the structure of zeolite Beta, said contacting being effected under a combination of conditions effective to selectively form said ether.
U.S. Pat. No. 5,225,609 to Bell discloses a process for the production of alkyl tertiary alkyl ether employing a zeolite catalyst, particularly zeolite beta which is pretreated either by steaming or hydrothermal treatment using liquid water at elevated temperatures. This process is claimed to be particularly effective in reducing the formation of dimer by-product in the zeolite Beta catalyzed process for the formation of methyl tertiary butyl ether (MTBE) with high selectivity.
The use of faujasite zeolites in alkyl ether formation is also known in the art. The following references discuss the use of faujasite zeolites in various applications.
Japanese Patent 82-07432 teaches the use of zeolites, particularly mordenites and faujasites, to make dialkyl ethers containing primary or secondary alkyl groups by the liquid phase dehydration of alcohols.
In allowed U.S. Pat. No. 5,214,217, to Texaco Chemical Company, there is disclosed a method for preparing methyl tertiary butyl ether by reacting butanol and methanol in the presence of a catalyst comprising a super-acid alumina or a faujasite-type zeolite.
In U.S. Pat. No. 5,081,318, a Y-type zeolite modified with fluorosulfonic acid is disclosed.
In U.S. Pat. No. 3,955,939, to Sommer et al. (1976), there is disclosed the production of a water-free mixture of isopropyl alcohol, diisopropyl alcohol, diisopropyl ether and by-products by the catalytic hydration of propylene in the gaseous phase at temperatures of 140.degree. -170.degree. C., in the presence of a catalyst comprising a super-acid alumina or a faujasite-type zeolite.
It is also known in the art to produce IPA and DIPE by the hydration of propylene and subsequent dehydration of IPA to DIPE.
In U.S. Pat. No. 5,208,387, also to Harandi et al., there is disclosed a process for the acid catalyzed production of DIPE from propene and water feed stream that eliminates the propene recycle stream to the olefin hydration reactor and achieves high propene conversion. This process is carried out in two stages wherein the first stage comprises a zeolite catalyzed hydration and etherification of propene employing a minimum of water feed and the second stage converts unconverted propene from the first stage reactor by hydration and etherification to DIPE.
In an article titled "Race to License New MTBE and TAME Routes Heats Up", Rotman D., Chemical Week, Jan. 6, 1993, p. 48, there is a review of new technology at several different companies which centers around skeletal isomerization, particularly of C.sub.4 and C.sub.5 olefins. The interest in this technology is fueled by the promise of dramatically increased and relatively inexpensive isobutylene and isoamylene that could boost MTBE and TAME production, often constrained by the amounts of available isobutylene in refinery or steam cracker streams. DIPE production from propylene is also discussed.
Mobil Corp. has disclosed new etherification technology that can produce fuel oxygenates based only on olefinic refinery streams and water. This process has the potential to allow refiners to produce oxygenates without having to rely on an external supply of alcohols. The technology is developed around diisopropyl ether (DIPE) based on propylene. Wood, A., supra, p. 7.
In related U.S. Pat. No. 5,449,838 there is disclosed a two-step process for generation of isopropyl t-butyl ether from crude acetone.
In related U.S. Pat. No. 5,430,198 there is disclosed a two-step process for the generation of diisopropyl ether from a crude by-product acetone stream which comprises hydrogenating said crude acetone over a bulk metal, nickel-rich catalyst to give an isopropanol effluent and subjecting said isopropanol-rich intermediate to dehydration conditions in the presence of a strong acid zeolite catalyst. This process requires interstage separation of the hydrogen prior to the dehydration step. In related U.S. Pat. No. 5,476,972 discloses a one-step process for the generation of DIPE from a crude acetone by-product stream using a single bifunctional catalyst which contains both hydrogenation and etherification activity.
It does not appear that there is any disclosure or suggestion in the art of converting acetone to ethers in an integrated process having a catalyst configuration wherein a hydrogenation activity gradient exists along the reactor bed in one direction and an etherification activity gradient exists along the bed in the other direction.
The by-product stream containing low-value crude acetone typically contains about 20% to 80% acetone. The by-product acetone stream may also contain greater than 5% of both methanol (MeOH) and t-butanol (tBA) and typically in the range of 10% to 40% methanol and t-butanol. It would greatly enhance the economics of any process to produce MTBE or other oxygenates if acetone, along with some methanol and t-butanol, from a by-product stream could be converted to oxygenates such as DIPE, IPTBE and MTBE.